This invention relates generally to level measurement, and more particularly to an inclination gauge providing both a digital and an analog read-out.
As used in mechanics, level is a term referring to any direction that is at right angles to the force of gravity. Because of the earth's curvature, this direction is not precisely horizontal, but the deviation from the horizontal is negligible for short distances. The tool kit of any competent bricklayer or carpenter invariably includes a spirit level. However, the use of such levels is by no means limited to the field of construction, for this level is an essential component of many delicate physical, astronomical and engineering instruments.
Operation of the spirit level depends on the simple principle that an air bubble seeks the highest point in a container enclosing the liquid in which the bubble is formed. In a standard spirit level, the glass tube housing the liquid is either slightly curved with its convex side upward, or the tube is ground with a curved inner bore.
The glass tube is supported on a rigid base or bar, and the bubble therein always comes to equilibrium at the same point whenever the bar has the same slope with respect to the horizontal plane. By providing the spirit level tube with a graduated scale, the level may be made a sensitive gauge for measuring changes in the angle of inclination.
From the practical standpoint, the value of a spirit level in providing an accurate indication of inclination depends on the ability of the user to discern the precise position of the air bubble with respect to the scale indicia on the tube. While the condition of the user's eyesight is a factor in this regard, as well as the angle at which he views the bubble, for many ordinary level applications, the fact that the readings taken by the user are somewhat inexact may not be a serious drawback; but in other situations, even a slight error cannot be tolerated.
But whether or not the user of the spirit level is capable of reading the level without difficulty, the fact is that the user, in order to obtain a correct reading, must exercise care, and this consumes time--which, in a procedure requiring frequent level readings, adds materially to the cost of the operation.
While the invention will be described in connection with an inclination gauge which supplants or supplements conventional spirit levels of the type used in the construction industry, it is to be understood that the gauge in accordance with the invention is also useful as a surveyor's level attachable to a telescope to determine differences in elevation, and in other instruments which entail the measurement of inclination.
There are many prior patents which deal with so-called "inclinometers" to measure the magnitude and direction of inclination with respect to the force of gravity and to produce an electrical value in accordance therewith. Among these patents are the following:
Rickert U.S. Pat. No. 2,759,272;
Stimler U.S. Pat. No. 2,722,056;
Shea U.S. Pat. No. 2,893,134;
Harris U.S. Pat. No. 3,490,153;
Cothran U.S. Pat. No. 3,478,437;
Foody U.S. Pat. No. 3,114,209;
Remington U.S. Pat. No. 3,487,303;
Holderer U.S. Pat. 3,164,023
Bauer U.S. Pat. No. 3,559,294;
Shawhan U.S. Pat. No. 3,906,471;
Shawhan U.S. Pat. No. 3,766,658;
Remington U.S. Pat. No. 3,442,023.